This article sheds light on the dynamics of power in a contested field of action - environmental assessment (EA) - within which theorisation and analysis of power has been limited, and there has been little engagement with productive approaches to power. We use of a typology for analysing the production of social order to create a rich and complex narrative of the power dimensions of the institutionalisation of EA systems, and thereby to problematise this field of action. The analysis focuses upon the World Bank's pursuit of its strategy of reshaping governance in developing countries through the development of a new instrument for EA - Institution-centred Strategic Environmental Assessment (ISEA). We examine the Bank's experimentation with ISEA as an instrument for the critique, unsettling and potential reform of environmental governance in developing countries, and as a mechanism for reinforcing its status as a leading authority on development. This situated analysis opens the way towards a richer understanding of power dynamics in the field of EA, from which a clearer understanding of the normative challenges within this field of action can be developed. In so doing, it also raises the vexed question of how concepts and technologies of governance have permeated environment and development thinking with so little critical scrutiny.